The field of art to which the invention pertains includes power steering systems, and more specifically power steering systems for electric vehicles.
Power steering systems for electrically powered industrial trucks and the like are frequently of the open center type; these require circulating hydraulic fluid to be continuously available for power steering demands of the operator. Typically, when the ignition switch is on and the dead man seat switch is activated, as in electric industrial lift trucks, an electric steer motor drives a fixed displacement, gear-type hydraulic pump. So long as these two switches are on, the motor and pump are running even though no steering demands are made. The continuous operation of the steer motor and pump is objectionable because it results in excessive wear of these components, excessive power consumption, which is particularly disadvantageous in battery driven electric vehicles, and the generation of objectionable heat and noise.